1. Field of the Invention:
The present invention relates generally to handover between different systems. More particularly, but not exclusively, the present invention relates to a method and apparatus for facilitating handover between a legacy Universal Mobile Telecommunication Service (UMTS) system and an Enhanced UMTS (E-UMTS) system.
2. Description of the Related Art:
A Universal Mobile Telecommunication Service (UMTS) system is the 3rd generation asynchronous mobile communication system that is based on Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS). A UMTS system uses Wideband Code Division Multiple Access (CDMA) as Radio Access Technology (RAT) and provides coherent service in which users of mobile phones or computers can transmit packet-based text, digitalized audio/video and multimedia data at a rate of 2 Mbps or higher anyplace in the world. The UMTS system employs the virtual access concept called the packet-switched access which uses a packet protocol such as the Internet Protocol (IP), and can always access any terminal in the network.
FIG. 1 illustrates a configuration of a conventional UMTS system.
Referring to FIG. 1, a User Equipment (UE) 110 refers to a terminal device or a user participating in wireless communication, and is wirelessly connected to a Node B 120. The Node B 120, a wireless base transceiver station for directly participating in communication with the UE 110, manages its associated cells. A Radio Network Controller (RNC) 130 controls a plurality of Node Bs and determines whether a need for handover exists. The connection between the RNC 130 and the UE 110 is made by a Radio Resource Control (RRC) interface.
The RNC 130 is connected to a Packet Switched or Packet Service (PS) network, such as the Internet, by a Serving GPRS Support Node (SGSN) 140. The communication between the RNC 130 and the PS network is achieved by Packet Switched Signaling (PS Signaling). The connection between the RNC 130 and the SGSN 140 is called an “Iu-PS interface”. The SGSN 140 controls the service provided to each of the subscribers. Typically, the SGSN 140 manages service accounting-related data of each subscriber, and selectively transmits/receives the data to be exchanged with the UE 110 via the Serving RNC (SRNC) 130 that manages the corresponding UE 110.
A Gateway GPRS Support Node (GGSN) 150 serves as a gateway node that allocates an IP address to the UE 110 receiving packet service and connects the UE 110 to an external Packet Data Network (PDN) 160.
As shown in FIG. 1, a combination of the Node B 120 and the RNC 130 is referred to as a Radio Access Network (RAN) 170, and a combination of the SGSN 140 and the GGSN 150 is referred to as a Core Network (CN) 180. Each SGSN 140 and each GGSN 150 is called a CN node.
An E-UMTS system, improved from the CDMA-based UMTS system, employs Orthogonal Frequency Division Modulation (OFDM), and reduces the number of network nodes necessary to connect the UE to the PDN. This facilitates fast data transmission.
FIG. 2 illustrates an exemplary configuration of an E-UMTS system.
Referring to FIG. 2, a UE 210 represents a terminal device or a user. An Enhanced RAN (E-RAN) 240 serves as the Node B 120 and the RNC 130 in the legacy UMTS system. In the E-RAN 240, like in the legacy UMTS system, functions of an E-Node B 220 and an E-RNC 230 may be physically separated in different nodes. Alternatively, functions of an E-Node B 220 and an E-RNC 230 can be integrated in one physical node. An E-CN 250, a combined node of the SGSN 140 and the GGSN 150 in the legacy UMTS system, is situated between a PDN 260 and the E-RAN 240. The E-CN 250 serves as a gateway node for allocating an IP address to the UE 210 and for connecting the UE 210 to the PDN 260.
Service areas of the legacy UMTS system and the E-UMTS system may overlap each other. In the overlapping service area (also known as a handover area), a dual-mode UE capable of receiving signals from both the legacy UMTS system and the E-UMTS system must perform handover between the two systems. To provide services to users via the E-UMTS system, the service provider requires the handover procedure between the legacy UMTS system and the E-UMTS system.
Accordingly, there is a need for an improved system and method of facilitating handover between a legacy Universal Mobile Telecommunication Service (UMTS) system and an Enhanced UMTS (E-UMTS) system.